package x.org.bouncycastle.crypto.digests;


import x.org.bouncycastle.crypto.util.Pack;
import x.org.bouncycastle.util.Memoable;

/**
 * FIPS 180-2 implementation of SHA-256.
 * 
 * <pre>
 *         block  word  digest
 * SHA-1   512    32    160
 * SHA-256 512    32    256
 * SHA-384 1024   64    384
 * SHA-512 1024   64    512
 * </pre>
 */
public class SHA256Digest extends GeneralDigest {
	
	private static final int DIGEST_LENGTH = 32;

	private int H1, H2, H3, H4, H5, H6, H7, H8;

	private int[] X = new int[64];
	private int xOff;

	/**
	 * Standard constructor
	 */
	public SHA256Digest() {
		reset();
	}

	/**
	 * Copy constructor. This will copy the state of the provided message
	 * digest.
	 */
	public SHA256Digest(SHA256Digest t) {
		super(t);

		copyIn(t);
	}

	private void copyIn(SHA256Digest t) {
		super.copyIn(t);

		H1 = t.H1;
		H2 = t.H2;
		H3 = t.H3;
		H4 = t.H4;
		H5 = t.H5;
		H6 = t.H6;
		H7 = t.H7;
		H8 = t.H8;

		System.arraycopy(t.X, 0, X, 0, t.X.length);
		xOff = t.xOff;
	}

	public String getAlgorithmName() {
		return "SHA-256";
	}

	public int getDigestSize() {
		return DIGEST_LENGTH;
	}

	protected void processWord(byte[] in, int inOff) {
		// Note: Inlined for performance
		// X[xOff] = Pack.bigEndianToInt(in, inOff);
		int n = in[inOff] << 24;
		n |= (in[++inOff] & 0xff) << 16;
		n |= (in[++inOff] & 0xff) << 8;
		n |= (in[++inOff] & 0xff);
		X[xOff] = n;

		if (++xOff == 16) {
			processBlock();
		}
	}

	protected void processLength(long bitLength) {
		if (xOff > 14) {
			processBlock();
		}

		X[14] = (int) (bitLength >>> 32);
		X[15] = (int) (bitLength & 0xffffffff);
	}

	public int doFinal(byte[] out, int outOff) {
		finish();

		Pack.intToBigEndian(H1, out, outOff);
		Pack.intToBigEndian(H2, out, outOff + 4);
		Pack.intToBigEndian(H3, out, outOff + 8);
		Pack.intToBigEndian(H4, out, outOff + 12);
		Pack.intToBigEndian(H5, out, outOff + 16);
		Pack.intToBigEndian(H6, out, outOff + 20);
		Pack.intToBigEndian(H7, out, outOff + 24);
		Pack.intToBigEndian(H8, out, outOff + 28);

		reset();

		return DIGEST_LENGTH;
	}

	/**
	 * reset the chaining variables
	 */
	public void reset() {
		super.reset();

		/*
		 * SHA-256 initial hash value The first 32 bits of the fractional parts
		 * of the square roots of the first eight prime numbers
		 */

		H1 = 0x6a09e667;
		H2 = 0xbb67ae85;
		H3 = 0x3c6ef372;
		H4 = 0xa54ff53a;
		H5 = 0x510e527f;
		H6 = 0x9b05688c;
		H7 = 0x1f83d9ab;
		H8 = 0x5be0cd19;

		xOff = 0;
		for (int i = 0; i != X.length; i++) {
			X[i] = 0;
		}
	}

	protected void processBlock() {
		//
		// expand 16 word block into 64 word blocks.
		//
		for (int t = 16; t <= 63; t++) {
			X[t] = Theta1(X[t - 2]) + X[t - 7] + Theta0(X[t - 15]) + X[t - 16];
		}

		//
		// set up working variables.
		//
		int a = H1;
		int b = H2;
		int c = H3;
		int d = H4;
		int e = H5;
		int f = H6;
		int g = H7;
		int h = H8;

		int t = 0;
		for (int i = 0; i < 8; i++) {
			// t = 8 * i
			h += Sum1(e) + Ch(e, f, g) + K[t] + X[t];
			d += h;
			h += Sum0(a) + Maj(a, b, c);
			++t;

			// t = 8 * i + 1
			g += Sum1(d) + Ch(d, e, f) + K[t] + X[t];
			c += g;
			g += Sum0(h) + Maj(h, a, b);
			++t;

			// t = 8 * i + 2
			f += Sum1(c) + Ch(c, d, e) + K[t] + X[t];
			b += f;
			f += Sum0(g) + Maj(g, h, a);
			++t;

			// t = 8 * i + 3
			e += Sum1(b) + Ch(b, c, d) + K[t] + X[t];
			a += e;
			e += Sum0(f) + Maj(f, g, h);
			++t;

			// t = 8 * i + 4
			d += Sum1(a) + Ch(a, b, c) + K[t] + X[t];
			h += d;
			d += Sum0(e) + Maj(e, f, g);
			++t;

			// t = 8 * i + 5
			c += Sum1(h) + Ch(h, a, b) + K[t] + X[t];
			g += c;
			c += Sum0(d) + Maj(d, e, f);
			++t;

			// t = 8 * i + 6
			b += Sum1(g) + Ch(g, h, a) + K[t] + X[t];
			f += b;
			b += Sum0(c) + Maj(c, d, e);
			++t;

			// t = 8 * i + 7
			a += Sum1(f) + Ch(f, g, h) + K[t] + X[t];
			e += a;
			a += Sum0(b) + Maj(b, c, d);
			++t;
		}

		H1 += a;
		H2 += b;
		H3 += c;
		H4 += d;
		H5 += e;
		H6 += f;
		H7 += g;
		H8 += h;

		//
		// reset the offset and clean out the word buffer.
		//
		xOff = 0;
		for (int i = 0; i < 16; i++) {
			X[i] = 0;
		}
	}

	/* SHA-256 functions */
	private int Ch(int x, int y, int z) {
		return (x & y) ^ ((~x) & z);
	}

	private int Maj(int x, int y, int z) {
		return (x & y) ^ (x & z) ^ (y & z);
	}

	private int Sum0(int x) {
		return ((x >>> 2) | (x << 30)) ^ ((x >>> 13) | (x << 19))
				^ ((x >>> 22) | (x << 10));
	}

	private int Sum1(int x) {
		return ((x >>> 6) | (x << 26)) ^ ((x >>> 11) | (x << 21))
				^ ((x >>> 25) | (x << 7));
	}

	private int Theta0(int x) {
		return ((x >>> 7) | (x << 25)) ^ ((x >>> 18) | (x << 14)) ^ (x >>> 3);
	}

	private int Theta1(int x) {
		return ((x >>> 17) | (x << 15)) ^ ((x >>> 19) | (x << 13)) ^ (x >>> 10);
	}

	/*
	 * SHA-256 Constants (represent the first 32 bits of the fractional parts of
	 * the cube roots of the first sixty-four prime numbers)
	 */
	static final int K[] = { 0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
			0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5, 0xd807aa98,
			0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe,
			0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786, 0x0fc19dc6,
			0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
			0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3,
			0xd5a79147, 0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138,
			0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e,
			0x92722c85, 0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
			0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070, 0x19a4c116,
			0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a,
			0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814,
			0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2 };

	public Memoable copy() {
		return new SHA256Digest(this);
	}

	public void reset(Memoable other) {
		SHA256Digest d = (SHA256Digest) other;

		copyIn(d);
	}
}
